U.S. patent application number 12/282104 was filed with the patent office on 2009-03-19 for chip type semiconductor light emitting device.
This patent application is currently assigned to ROHM CO., LTD.. Invention is credited to Tomio Inoue.
Application Number | 20090072250 12/282104 |
Document ID | / |
Family ID | 38474957 |
Filed Date | 2009-03-19 |
United States Patent
Application |
20090072250 |
Kind Code |
A1 |
Inoue; Tomio |
March 19, 2009 |
CHIP TYPE SEMICONDUCTOR LIGHT EMITTING DEVICE
Abstract
There is provided a reflective chip type semiconductor light
emitting device, which has improved efficiency of taking out light
and further improved luminance with the same input, and which emits
high luminance light by emitting light uniformly from an area as
large as possible and is suitable for lighting apparatuses. A pair
of terminal electrodes (11, 12) is provided at the both end
portions of one surface (front surface) of a substrate (1) so as to
be electrically separated, and a plurality of LED chips (2) are
separately provided on the one surface (front surface) of the
substrate (1). Each of the LED chips (2) is electrically connected
to a first terminal electrode (11) through a first bonding section
(11a), and to a second terminal electrode (12) through a wire (7)
and a second bonding section (12a), respectively. A reflecting wall
(3) is provided so as to surround a circumference of each of the
plurality of LED chips (2) on the one surface (front surface) of
the substrate (1).
Inventors: |
Inoue; Tomio; (Kagoshima,
JP) |
Correspondence
Address: |
RABIN & Berdo, PC
1101 14TH STREET, NW, SUITE 500
WASHINGTON
DC
20005
US
|
Assignee: |
ROHM CO., LTD.
Kyoto-shi
JP
|
Family ID: |
38474957 |
Appl. No.: |
12/282104 |
Filed: |
March 7, 2007 |
PCT Filed: |
March 7, 2007 |
PCT NO: |
PCT/JP2007/054409 |
371 Date: |
October 6, 2008 |
Current U.S.
Class: |
257/88 ;
257/E33.067 |
Current CPC
Class: |
H01L 33/60 20130101;
H01L 2224/48247 20130101; H01L 2224/45144 20130101; H01L 2224/48091
20130101; H01L 2224/45144 20130101; H01L 33/46 20130101; H01L
25/0753 20130101; H01L 2224/48091 20130101; H01L 2224/48091
20130101; H01L 2924/00 20130101; H01L 2224/48257 20130101; H01L
2924/00 20130101; H01L 2924/00014 20130101 |
Class at
Publication: |
257/88 ;
257/E33.067 |
International
Class: |
H01L 33/00 20060101
H01L033/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 8, 2006 |
JP |
2006-062691 |
Claims
1. A chip type semiconductor light emitting device comprising: a
substrate; a pair of terminal electrodes provided electrically
separately at both end portions of one surface of the substrate
which are opposite to each other; a plurality of light emitting
device chips provided separately on the one surface of the
substrate and connected to the pair of terminal electrodes; and a
reflecting wall provided so as to surround a surrounding of each of
the plurality of light emitting device chips.
2. The chip type semiconductor light emitting device according to
claim 1, wherein the reflecting wall surrounding each of the light
emitting device chips is formed so that an inner circumference of
the reflecting wall at a side of the light emitting device chips is
smaller than that at a front surface side away from the light
emitting device chips.
3. The chip type semiconductor light emitting device according to
claim 1, wherein at least a part of the reflecting wall is formed
with a laminated body formed by coating a paste material.
4. The chip type semiconductor light emitting device according to
claim 3, wherein the part of the reflecting wall is formed by
forming the laminated body of the reflecting wall stepwise, thereby
an inner circumference of the reflecting wall at a side of the
light emitting device chips is smaller than that at a front surface
side away from the light emitting device chips.
5. The chip type semiconductor light emitting device according to
claim 1, wherein a part of the reflecting wall between adjacent two
of the plurality of light emitting device chips is formed with a
laminated body formed by coating a paste material and the other
part of the reflecting wall which is at an outer circumference of
the entire of the plurality of light emitting device chips is
formed with a reflecting case which is formed separately and fixed
to the substrate.
6. The chip type semiconductor light emitting device according to
claim 3, wherein both of the substrate and the part of the
reflecting wall are formed with a material whose principal material
is a sintered body of alumina.
7. The chip type semiconductor light emitting device according to
claim 1, wherein a through hole is formed at a position of the
substrate where each of the light emitting device chips is to be
provided and the through hole is filled with a material having a
larger thermal conductivity than that of the substrate, thereby a
through hole for heat dissipation is formed.
8. The chip type semiconductor light emitting device according to
claim 7, wherein the through hole is filled with electrically
conductive material, one electrode of each of the light emitting
device chips is connected to a back surface electrode provided on a
back surface of the substrate through the through hole for heat
dissipation, and the back surface electrode is connected to one of
the pair of terminal electrodes.
9. The chip type semiconductor light emitting device according to
claim 1, wherein each of the light emitting device chips is formed
in a quadrilateral shape having a size such that one side of a
front surface or a back surface of each of the light emitting
device chips is 0.2 to 0.4 mm.
10. The chip type semiconductor light emitting device according to
claim 1, wherein a shape of a longitudinal cross section of each of
the light emitting device chips mounted on the one surface of the
substrate is trapezoidal, and each of the light emitting device
chips is mounted on the substrate so that a side of the substrate
is a long side of the trapezoid and a surface side opposite to the
substrate is a short side.
11. The chip type semiconductor light emitting device according to
claim 1, wherein each of the light emitting device chips is formed
so as to emit blue light or ultraviolet light, and a light
transmitting resin containing a light color conversion member which
converts the emitted light to white light is provided on each of
the light emitting device chips.
12. The chip type semiconductor light emitting device according to
claim 1, wherein the plurality of light emitting device chips are
connected in parallel between the pair of terminal electrodes.
13. The chip type semiconductor light emitting device according to
claim 1, wherein the plurality of light emitting device chips are
connected in series between the pair of terminal electrodes.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a chip type (surface mount
type) semiconductor light emitting device which is provided with a
pair of terminal electrodes (including leads) at both end portions
on a substrate and a plurality of light emitting device chips
(hereinafter referred to as LED chips) on the substrate. More
particularly, the present invention relates to a chip type
semiconductor light emitting device in which, even in a
semiconductor light emitting device capable of high luminance light
emitting with high current drive and an enlarged light emitting
area, high luminance can be obtained by improving efficiency of
taking out light further.
BACKGROUND OF THE INVENTION
[0002] For example, a chip type semiconductor light emitting device
by the prior art is formed, as shown in FIG. 5(a), by providing a
pair of terminal electrodes 42 and 43 at both end portions of a
substrate 41 made of a BT resin or the like so as to be extended to
a back surface of the substrate 41, connecting a lower electrode of
a LED chip 44 to one terminal electrode 42 by die-bonding the LED
chip 44 on the one terminal electrode 42, and connecting an upper
electrode of the LED chip 44 to another terminal electrode 43 with
a wire 45. A surrounding thereof is surrounded with a reflecting
case 46, which is formed of a resin made of a liquid polymer or the
like, so as to reflect light toward a front side, and a sealing
resin layer 47 is formed by filling a light transmitting resin
inside (cf. for example PATENT DOCUMENT 1).
[0003] In addition, in recent years, since development of a white
semiconductor light emitting device has been advanced and
semiconductor light emitting devices have been used for lighting
apparatuses or the like, as for the chip type semiconductor light
emitting device, further improving of luminance is expected and
high current drive has been realized with enlarging a chip size
and, at the same time, increasing input power. Therefore, since
heat generation in LED chips increases, it is necessary to inhibit
lowering of the luminance caused by thermal saturation even when
high current is applied and also to improve heat dissipation
characteristics. As an example of a semiconductor light emitting
device for such high current use with a chip type (surface mount
type), having a reflecting case at a surrounding, and having heat
dissipation characteristics, a structure shown in FIG. 5(b) has
been introduced.
[0004] Namely, in FIG. 5(b), a resin portion 52 integrating a
reflecting case 57 with a substrate 51 at a surrounding of the
substrate 51 which has a large thermal conductivity such as, for
example, that of AlN, and an insulating property, is provided
fixing a pair of leads 53 and 54, a LED chip 55 emitting, for
example, blue light and having a large size of, for example, 0.9
mm.times.0.9 mm is mounted on the lead 53 of one side, and,
similarly to the above-described example, a pair of electrodes of
the LED chip 55 are electrically connected to the pair of leads 53
and 54 with a wire 56 made of gold or the like. A reflecting case
57 made of, for example, a white resin (for example, AMODEL) is
formed at a surrounding of the LED chip 55 and a wire bonding
portion, and the reflecting case 57 and the resin portion 52 are
formed of the white resin by injection molding concurrently. Then,
a portion of the LED chip 55 and the wire 56 surrounded by the
reflecting case 57 is coated by a light color conversion resin
layer 58 formed by coating a light color conversion resin
containing a fluorescent material which converts a part of blue
light into red light and green light in order to emit white light
by mixing them.
PATENT DOCUMENT 1: Japanese Patent Application Laid-Open No.
2001-177155
DISCLOSURE OF THE INVENTION
Problem to be Solved by the Present Invention
[0005] As described above, in a reflective chip type semiconductor
light emitting device for high current drive by the prior art,
luminance is improved by using a LED of a large chip size. However,
if an area of the chip is increased, light emitted at a center
portion of the chip and traveling laterally is absorbed by
semiconductor layers and attenuates, and the luminance can not be
improved sufficiently. In addition, even if a LED of a large size
is used, the size has a limitation, then there is a problem such
that luminance is not sufficient for a chip type semiconductor
light emitting device for lighting apparatuses. Furthermore, in a
lighting apparatus or the like which is required to light a large
area uniformly, since an area emitting light is a small point shape
of 0.9 mm square even if a chip size is increased, there is a
problem such that the chip type semiconductor light emitting device
is not suitable for surface light sources such as lighting
apparatuses or the like. In addition, as quantity of heat
generation accompanied with enhancing luminance increases
remarkably, heat dissipation at a center portion of the LED chip
deteriorates additionally by enlarging the chip size, and there
arises a problem such that reliability is lowered by breakage of
the LED chip or deterioration of characteristics, caused by
heat.
[0006] In addition, if a metal plate or an AlN insulating substrate
of a high thermal conductivity is used at a principal portion of
the substrate of the chip type semiconductor light emitting device,
not only there is a problem of processability or a cost, but also
there is a problem such that sufficient heat dissipation can not be
achieved if a material having a high thermal conductivity is not
provided at a mounting board side on which the chip type
semiconductor light emitting device is to be mounted so as to be
contacted with the substrate of the chip type semiconductor light
emitting device, even if the thermal conductivity of the substrate
of the chip type semiconductor light emitting device is high. In
addition, if the reflecting case exposed to the front surface side
by a large area is formed with a white resin, a thermal
conductivity of the reflecting case is small by 1/1,000 comparing
to the metal plate, and heat dissipation characteristics from the
reflecting case is very inferior, thereby there arises a problem
such that the heat dissipation from the reflecting case is not
sufficient. Further, if coefficients of thermal expansion of the
substrate and the reflecting case are different, peeling between
both occurs by heat cycles and the heat dissipation becomes more
inferior.
[0007] The present invention is directed to solve the
above-described problems and an object of the present invention is
to provide a reflective chip type semiconductor light emitting
device, which has improved efficiency of taking out light and
further improved luminance with the same input, and which emits
high luminance light by emitting light uniformly from an area as
large as possible and is suitable for lighting apparatuses.
[0008] Another object of the present invention is to provide a
reflective chip type semiconductor light emitting device capable of
improving reliability against heat generation by further improving
the heat dissipation from the entire of the chip type semiconductor
light emitting device in addition to the above-described
object.
Means for Solving the Problem
[0009] A chip type semiconductor light emitting device according to
the present invention includes a substrate, a pair of terminal
electrodes provided electrically separately at both end portions of
one surface of the substrate which are opposite to each other, a
plurality of light emitting device chips provided separately on the
one surface of the substrate and connected to the pair of terminal
electrodes, and a reflecting wall provided so as to surround a
surrounding of each of the plurality of light emitting device
chips. Here, the terminal electrodes mean electrodes formed so as
to be connected to electrodes of the LED chip and to be connected
to the substrate or the like, and include electrodes formed with a
metal film on the substrate, leads formed separately and provided
on the substrate by adhesion or mounting, or the like.
[0010] At least a part of the reflecting wall is formed with a
laminated body formed by coating a paste material, thereby the
reflecting wall can be formed accurately even on a small region. In
addition, the laminated body can be fixed by repeating coating and
drying, and finally by baking or firing.
[0011] It is preferable that both of the substrate and the part of
the reflecting wall are formed with a material whose principal
material is a sintered body of alumina, because heat dissipation
characteristics can be improved. Here, the principal material means
that at least 50% or more of the substrate or the like is a
sintered body of alumina, and other materials, impurities or the
like may be included to some extent.
[0012] In addition, it is preferable that a through hole is formed
at a position of the substrate where each of the light emitting
device chips is to be provided and the through hole is filled with
a material having a larger thermal conductivity than that of the
substrate, because the heat dissipation characteristics can be more
improved.
EFFECT OF THE INVENTION
[0013] According to the present invention, in the reflective chip
type semiconductor light emitting device, LED chips divided into a
plurality of chips are provided on separated regions of the
substrate, and a surrounding of each of the LED chips is surrounded
by the reflecting wall (reflector), thereby an area of the chip
sides increases compared to that in one large chip, a total
quantity of light emitted from each side of the chips increases,
and light upward increases suitably. Namely, in one chip with a
large area, light emitted in a center portion and traveling
laterally is apt to attenuate by being absorbed by semiconductor
layers such as an active layer or the like, however, since the
chips are divided into a small size in the present invention, light
emitted in the center portion and traveling laterally is emitted
from the side and reflected upward by the reflecting wall and can
be utilized effectively. In addition, since not one LED chip but
small divided LED chips are dispersed in a large area of the
substrate, they acts not as light sources of a point shape but as a
surface light source, and emit mild light suitable for lighting
apparatuses. Further as for heat generation within the LED chips,
since the reflecting wall which can dissipate the heat is
respectively provided near the LED chips divided into a small size,
the heat can be dissipated through the substrate and the reflecting
wall at every small region and deterioration by heat can be
inhibited.
[0014] In addition, since a sintered body of alumina which has a
comparatively high thermal conductivity is used for the reflecting
wall and the substrate, there exists no problem caused by a
difference of thermal expansion between the substrate and the
reflecting wall, and heat can be dissipated fast by approximately
100 times compared to a case of a white resin, while maintaining
close contact. As a result, since the heat can be dissipated from
exposed surfaces of the reflecting wall having a large area, and
even in a case such as heat dissipation is not sufficient from the
substrate (regardless of heat dissipation characteristics of the
mounting board), the heat can be dissipated from the reflecting
wall, the heat dissipation characteristics of the LED is
significantly improved and reliability can be also improved
remarkably. In addition, since the reflecting wall is formed of an
inorganic material, a color of the reflecting wall hardly changes
even its temperature is raised, and an excellently stable
reflection coefficient can be maintained.
[0015] In addition, by forming a through hole at a position of the
substrate where each of the light emitting device chips is to be
provided and the through hole is filled with a material having a
larger thermal conductivity than that of the substrate, since heat
from the LED chip conducts to the mounting board rather through a
filling material embedded in the through hole than the sintered
body of alumina, thermal conductivity can be improved by the
substrate, then, in case such that a member having high thermal
conductivity is used for the mounting board, the heat dissipation
can be improved through the member.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is an explanatory figure of a plan view and a
cross-sectional view explaining an embodiment of the chip type
semiconductor light emitting device according to the present
invention.
[0017] FIG. 2 is an explanatory figure of a plan view explaining an
electrode pattern of the substrate using for the chip type
semiconductor light emitting device according to the present
invention.
[0018] FIG. 3 is an explanatory figure of a plan view and a
cross-sectional view explaining another embodiment of the chip type
semiconductor light emitting device according to the present
invention.
[0019] FIG. 4 is an explanatory cross-sectional view explaining of
a lamination structure of the LED chip shown in FIG. 1.
[0020] FIG. 5 is explanatory cross-sectional views showing examples
of a chip type semiconductor light emitting device by the prior
art.
EXPLANATION OF LTTERS AND NUMERALS
[0021] 1: substrate [0022] 2: LED chip [0023] 3: reflection wall
[0024] 4: through hole for heat dissipation [0025] 11: first
terminal electrode [0026] 12: second terminal electrode
THE BEST EMBODIMENT OF THE PRESENT INVENTION
[0027] An explanation will be given below of an embodiment of a
chip type semiconductor light emitting device according to the
present invention in reference to the drawings. As explanatory
figures of a plan view and cross-sectional views (cross-sectional
views at B-B and C-C of FIG. 1(a)) of an embodiment of the chip
type semiconductor light emitting device are shown respectively in
FIG. 1, a pair of terminal electrodes 11 and 12 is provided at the
both end portions of one surface (front surface) of a substrate 1
which are in opposite sides to each other so as to be electrically
separated, and a plurality (nine chips in the example shown in FIG.
1) of light emitting device chips (LED chips) 2 are separately
provided on the one surface (front surface, namely a plurality of
first bonding sections 11a which are electrically connected to the
first terminal electrode 11 through a back surface electrode 11b in
the example shown in FIG. 1) of the substrate 1. And a pair of
electrodes of each of the LED chips 2 is electrically connected to
the first terminal electrode 11 through the first bonding section
11a, and to the second terminal electrode 12 through a wire 7 and a
second bonding section 12a, respectively, and a reflecting wall 3
is provided so as to surround a surrounding of each of the
plurality of LED chips 2 on the one surface (front surface) of the
substrate 1. In addition, in the example shown in FIG. 1, the first
bonding sections 11a are formed at parts where the LED chips 2 are
to be provided on the substrate 1 made of a sintered body of
alumina as described later, and through holes are formed under the
first bonding sections 11a respectively. Through holes 4 for heat
dissipation are formed by filling the through holes (via contacts)
with a material such as silver or the like having a larger thermal
conductivity than that of the substrate 1, and lower electrodes of
the LED chips 2 are electrically connected to the first terminal
electrodes 11 through the first bonding sections, the through holes
4 for heat dissipation and the back surface electrode 11b provided
on the back surface of the substrate.
[0028] A substrate made of a sintered material of alumina is used
for the substrate 1, and a thickness thereof is similar to that of
a usual chip type semiconductor light emitting device and may be
approximately 0.06 to 0.5 mm. The substrate 1 is formed by
sintering a green sheet having a thickness of approximately 0.3 mm,
and, by forming metal films of the first and second terminal
electrodes 11 and 12, through holes la and 4 or the like, described
later, the substrate provided with the metal films or the like can
be obtained by sintering. If reflecting walls 3 described later are
formed with laminated bodys with alumina powder of a paste state,
at the time of sintering, the reflecting walls 3 can be
concurrently formed of alumina by sintering. The light emitting
device shown in FIG. 1(a) is formed with a size (outer shape) which
has (length).times.(width).times.(height) of approximately (3 to 5
mm).times.(3 to 5 mm).times.(1 to 3 mm).
[0029] On the surface of the substrate 1, the terminal electrodes
11 and 12, made of Ag, Au or the like, are formed, and an
explanation of patterns of the terminal electrodes 11 and 12 will
be given below in reference to FIG. 2 showing the back surface and
the surface of the substrate. As shown in a explanatory figure of
the back surface of the substrate of FIG. 2(a), the back surface
electrodes 11b and 12b are formed on the back surface of the
substrate 1, and the terminal electrodes 11 and 12 are connected to
the back surface electrodes 11b and 12b by side electrodes (not
shown in the figures) formed on inner sides of the through holes
1a, thereby a device of a surface mounting type is formed which is
mounted directly on a mounting board or the like by soldering or
the like.
[0030] In addition, the patterns of the first terminal electrode 11
and the second terminal electrode 12 of the surface side are
covered mostly with the reflecting wall 3 and only parts not
covered are drawn in the example shown in FIG. 1(a), however, as
shown by the explanatory figure of the substrate surface of FIG.
2(b), actually the first terminal electrode 11 is provided at two
corner side of four corners of the surface, the pattern is not to
connect the LED chips 2 directly to the first terminal electrode
11, and the LED chips 2 are connected to the first terminal
electrode 11 through the first bonding sections 11a electrically
connected to the first terminal electrode 11, the through holes 4
and the back surface electrodes 11b. on the other hand, the second
terminal electrode 12 is provided at another two corner side, where
the first terminal electrode 11 is not provided, on the surface,
and has the second bonding sections 12a reaching the vicinity of
the positions for providing the LED chips 2.
[0031] The first terminal electrode 11 and the second terminal
electrode 12 are not limited to this shape, and by forming the
through holes not at four corners but at a center part of each of
two sides opposing to each other, the first terminal electrode 11
and the second terminal electrode 12 may be formed so as to extend
only to opposing two sides. Further, the terminal electrodes 11 and
12 may be formed by providing lead frames or leads in place of such
metal films.
[0032] The first bonding sections 11a are formed at positions where
each of the plurality of LED chips 2 is to be arranged on the
surface of the substrate by patterning concurrently with the same
material as that of the terminal electrodes 11, 12 or the like, and
electrically connected to the first terminal electrode 11 through
the through holes 4 for heat dissipation filled with a electrically
conductive material having a larger thermal conductivity than that
of the substrate 1 made of silver or the like which are provided in
the through holes in the substrate 1 right under the first bonding
sections 11a, the back surface electrode 11b, and side electrodes
not shown in the figures formed on inner surfaces of the through
holes 1a of corners of the substrate where the first terminal
electrodes 11 is formed. In addition, the second bonding sections
12a are formed at the vicinity of the first bonding sections 11a as
parts of the second terminal electrode 12. In addition, since
number of the LED chips 2 may be also varied properly depending on
necessity, number or a shape of each of the bonding sections 11a
and 12a is varied properly correspondingly thereto.
[0033] In addition, a pattern shape of electrodes including the
first terminal electrode 11 and the second terminal electrode 12 of
FIG. 2 is an example for connecting the plurality of chips in
parallel, however other patterns may be allowed such as, for
example, a pattern in which the LED chips 2 are bonded to the first
terminal electrode 11 not through the back surface electrode 11b or
the through holes 4 for heat dissipation, and a pattern in which
the LED chips are bonded directly on the through holes 4 for heat
dissipation without providing the first bonding sections 11a. In
addition, in case of connecting the plurality of chips in series, a
pattern of the terminal electrodes can be changed freely so as to
form a series connection.
[0034] In the example shown in FIG. 1, at the parts of the
substrate 1 where the LED chips 2 are provided, namely right under
the first bonding sections 11a, through holes are formed, and the
through holes 4 for heat dissipation are formed by filling the
through holes with a metal such as Ag, Au, Cu or the like, or an
electrically conductive material having a larger thermal
conductivity than that of the substrate. The reason why the through
holes 4 are formed is that, in case of using a sintered body of
alumina for the substrate 1, the thermal conductivity is required
to be enhanced since the thermal conductivity becomes low comparing
to a metal substrate or an AlN substrate. In addition, it is to
realize a parallel connection simply by connecting the back surface
electrode 11b provided on the back surface of the substrate to the
pattern of the first bonding sections 11a provided on the surface
of the substrate. It is preferable that the through holes 4 are
provided with a diameter of, for example, approximately 0.1 to 0.5
mm and right under the first bonding sections 11a where each of the
LED chips 2 is bonded because heat dissipation of each of the LED
chips 2 can be achieved surely, and they may be changed properly.
By using such structure, heat dissipation by the thermal conduction
to the substrate 1 can be improved and, at the same time, the
plurality of chips can be simply connected in parallel.
[0035] LEDs emitting light of various colors can be used for the
LED chips 2, and, in order to obtain white light, a nitride
semiconductor light emitting device or the like emitting, for
example, blue light or ultraviolet light is used and a light
transmitting resin containing a light color conversion material is
coated on a surface thereof, thereby the white light can be
obtained. A size of each of the LED chips 2 is 0.3 mm square by
dividing, for example, a conventional chip of 0.9 mm square into
3.times.3 pieces. A size of wire bonding on the front surface is
required to be approximately 0.1 mm square, and then if number of
dividing is too large, there is no significance of dividing, and it
is preferable to divide so that one side is approximately 0.2 to
0.4 mm square. In the example, as shown in FIG. 4(b) described
later, the chips are formed in a trapezoid having a bottom surface
of 0.3 mm square and a front surface of 0.2 mm square. A
semiconductor constitution of the LED chips 2 is described
later.
[0036] The reflecting wall 3 is formed in order to condense light
emitted all round from each of the LED chips 2 toward a front side
and so as to surround each of the LED chips 2 in the example shown
in FIG. 1. Concretely, as shown in FIGS. 1(b) and 1(c), the
reflecting wall 3 is provided so as to surround the first bonding
section 11a where each of the LED chips 2 is provided and the
second bonding section 12a which is electrically connected to each
of the LED chips 2 with a wire or the like and formed with a
laminate body of a step shape so that a part thereof extends
slightly toward an outer side. Namely, the reflecting wall 3 has a
grid shape which is formed by hollowing out parts (the first
bonding section 11a and the second bonding section 12a) of the
substrate 1 where the LED chips 2 are provided, and the part of the
grid is formed with a laminated body having a step shape extending
slightly from inside. In addition, the part of the grid is formed
with a quadrilateral shape, and, at the same time, at an outer
periphery (outer periphery of the substrate 1) of the entire chip
type semiconductor light emitting device, with a shape
(quadrilateral shape in FIG. 1) corresponding to the shape of the
outer periphery the chip type semiconductor light emitting device.
Of course, the shape is not limited to this but may be varied
properly. In addition, number of the parts of the grid is nine in
the example shown in FIG. 1 because number of the LED chips 2 is
nine, but it may be varied properly according to the number of the
LED chips 2.
[0037] In addition, in the example shown in FIG. 1, the reflecting
wall 3 can not be stuck by being formed previously as a reflecting
case because it is very small, then, as described later, it is
formed by laminating a paste of alumina powder (green mint) or a
resin by a screen printing method, therefore it is formed with a
step shape. However, as in the example shown in FIG. 3, the
reflecting wall of the outer periphery can be stuck as the
reflecting wall 3 of a conventional type formed previously.
[0038] In addition, the reflecting wall 3 may be formed of a white
resin or the like, however it is preferably formed of a sintered
body of alumina, including the substrate 1, from the view point of
heat dissipation. In order to form the reflecting wall 3 of a
sintered body of alumina, by a screen printing method or the like a
paste of alumina powder is coated at a position, where the
reflecting wall 3 is formed, on the substrate 1, and dried
thereafter, by repeating the similar process thereon subsequently
with reducing sizes of the opening portions a little, a laminated
body is formed by laminating a plurality of layers of the green
sheet with a step shape, and thereafter they are sintered together.
In such manner, by forming the substrate 1 and the reflecting wall
3 are formed of the same sintered body of alumina, an adhesion
property of the substrate 1 and the reflecting wall 3 is superior,
and since, even though the sintered body of alumina is inferior in
the thermal conductivity compared to a metal plate or AlN, the
thermal conductivity is higher than that of the white resin used
for a conventional reflecting case by approximately 100 times, heat
generated in the LED chips 2 can be transmitted fast from the
substrate to the reflecting wall 3, therefore the heat can be
dissipated from a large area of the reflecting wall 3.
[0039] In addition, the substrate 1 made of the sintered body of
alumina has a lower thermal conductivity by approximately one order
compared to a metal plate or AlN, however, since heat conduction
from the substrate 1 to the mounting board is different according
to the mounting board, the sufficient heat conduction to the
mounting board can not be always obtained. However, since the heat
transmitted to the reflecting wall 3 is dissipated from a large
surface area surely, stable heat dissipation can be achieved, and,
at the same time, by constituting the substrate 1 and the
reflecting wall 3 with the same material, since peeling or the like
does not occur because coefficients of the thermal expansion are
same, the heat can be dissipated efficiently from the reflecting
wall 3, and the efficiency of heat dissipation can be improved in
total. Especially, as in the present invention, in case of
providing the reflecting wall 3 at each of the plurality of chips,
since heat dissipation at the reflecting wall 3 has a large
influence to heat dissipation characteristics of the chip type
semiconductor light emitting device, forming both of the substrate
1 and the reflecting wall 3 with a sintered body of alumina is very
effective.
[0040] FIG. 3 are explanatory figures of a plan view and
cross-sectional views (cross-sectional views at B-B and C-C in FIG.
3(a)) of another embodiment of the present invention. In this
example, the reflecting wall 3 provided at a region except an outer
periphery of the substrate 1 are formed by the above-described
screen printing method or the like, and thereafter the reflecting
case 3a previously formed is stuck only at the outer periphery with
a glass binder or the like. In addition, letters and numerals of
parts similar to those in FIG. 1 are attached and the explanation
is omitted here, however they are the same as those in the example
shown in FIG. 1. By using such constitution, since the reflecting
wall 3 provided between each of the LED chips 2 is formed by the
screen printing method which does not need a large space, the
reflecting case 3a which has a smooth inclined surface without any
irregularities similar to the conventional one can be stuck at the
outer periphery while being formed accurately even in a small space
between each of the LED chips 2. Furthermore, since the tall
reflection case 3a can be stuck at the periphery, even light which
can not be reflected sufficiently by the short reflection wall 3
having irregularities can be utilized by being reflected toward the
front surface side perfectly by the reflecting case 3a, and
luminance can be more improved.
[0041] In the examples shown in FIGS. 1 and 3, the LED chips 2
emitting blue light are used, and as an example of a
cross-sectional constitution is shown, for example, in FIG. 4(a),
LEDs using nitride semiconductor are formed. However, not being
limited to the example, a zinc oxide based (ZnO based) compound or
the like may be used. When the chip type semiconductor light
emitting device emitting white light is intended to be formed, in
case such that the LED chips 2 emit not blue light but ultraviolet
light, by coating a resin layer mixed with conversion members
(fluorescent material) converting the ultraviolet light into red
light, green light and blue light, white light can be also obtained
by mixing light of the three primary colors. Even the LED chip
emitting ultraviolet light can be similarly formed by using nitride
semiconductor or zinc oxide based compound.
[0042] Here, the nitride semiconductor means a compound of Ga of
group III element and N of group V element or a compound (nitride)
in which a part or all of Ga of group III element substituted by
other element of group III element like Al, In or the like and/or a
part of N of group V element substituted by other element of group
V element like P, As or the like. And, the zinc oxide (ZnO) based
compound semiconductor means an oxide including Zn, and means
concretely besides ZnO, an oxide of one or more elements of group
II A and Zn, an oxide of one or more elements of group II B and Zn,
or an oxide of elements of group IIA and group IIB and Zn.
[0043] The LED chips 2 are used for improving luminance, by
dividing a LED having a conventional size, which has
(length).times.(width).times.(height) of, for example,
approximately (0.9 mm).times.(0.9 mm).times.(0.12 mm) into nine,
the small LED chips 2 having a size which is, for example,
approximately (0.3 mm).times.(0.3 mm).times.(0.12 mm) are formed,
and the semiconductor light emitting device are formed by arranging
nine LED chips 2 on the substrate 1 in this case. Of course, a size
of chips by dividing can be varied corresponding to a size of the
chip type semiconductor light emitting device or the number of
chips to be provided on the substrate. In addition, in this
example, an outer shape of the LED chip 2 has a longitudinal
cross-section of trapezoidal (bottom surface of 0.3 mm square and
front surface of 0.2 mm square), however it may be a shape of a
rectangular solid or a cube. However, light is apt to be reflected
toward the front surface side by a taper shape. In order to form
with a trapezoidal shape, for example, at the time of dividing a
wafer into chips, by using a blade whose cross-section of a
thickness direction is trapezoidal, dicing grooves are formed in a
taper shape, then the LED chips 2 with the trapezoidal shape can be
obtained. In this case, as described later, if dicing is carried
out at a side of epitaxial growth layers, semiconductor layers are
apt to be damaged, therefore dicing is carried out from a substrate
side (thickness of the LED chip is almost thickness of the
substrate) and it is preferable to take out light from the
substrate side.
[0044] As shown in FIG. 4(a), the LED using nitride semiconductor
is provided with a low temperature buffer layer 22 made of, for
example, AlGaN based compound (which means various compound that a
mixed crystal ratio of Al is changed, including a case of zero and
the same applies hereinafter) and having a thickness of
approximately 0.005 to 0.1 .mu.m, for example, on an n-type SiC
substrate 21. And, there are laminated on the buffer layer 22 in
order, an n-type layer 23 made with, for example, an n-type GaN
layer or the like, of a thickness of approximately 1 to 5 .mu.m, an
active layer 24 having a thickness of approximately 0.05 to 0.3
.mu.m formed with a multiple quantum well (MQW) structure which is
formed by laminating 3 to 8 pairs of a well layer made of, for
example, In.sub.0.13Ga.sub.0.87N and having a thickness of 1 to 3
nm, and a barrier layer made of GaN and having a thickness of 10 to
20 nm, and a p-type layer 25 made with, for example, a p-type GaN
layer and having a thickness of approximately 0.2 to 0.3, thereby a
semiconductor lamination portion 29 is formed. Then, on a surface
of the p-type layer 25, a light transmitting conductive layer 26
made of, for example, ZnO is provided with a thickness of
approximately 0.1 to 10 .mu.m, on a part of a surface thereof, a
p-side electrode 27 is provided with a lamination structure of
Ti/Au, Pd/Au or the like with a total thickness of approximately
0.1 to 1 .mu.m, and an n-side electrode 28 is provided with a
lamination structure of Ti/Al or Ti/Au, or the like with a total
thickness of approximately 0.1 to 1 .mu.m. In addition, in case of
forming a chip of the above-described trapezoidal shape, as a
schematic view is shown in FIG. 4(b), it is preferable to form the
n-side electrode 28 small, the p-side electrode 27 large, and the
SiC substrate in a taper shape, so as to emit light from a back
surface side of the SiC substrate 21.
[0045] Although a SiC substrate is used as a substrate in the
above-described example, not being limited to the material, other
semiconductor substrate such as GaN, GaAs or the like can be used
and also a sapphire substrate can be used. In case of a
semiconductor substrate made of SiC or the like, as shown in FIG.
4, an electrode of one side can be provided on a back surface of
the substrate, however, in case of an insulating substrate made of
material such as sapphire, a conductivity type layer (n-type layer
23 in a constitution of FIG. 4(a)) of a lower layer is exposed by
removing a part of laminated semiconductor layers by etching, and
an electrode is formed on the exposed portion. In addition, in case
of using a semiconductor substrate, an n-type substrate is used and
an n-type layer is formed as a lower layer in the above-described
example, however the substrate and the lower layer may be formed so
as to have a p-type conductivity type. And, a material of the
buffer layer 22 is not limited to the AlGaN based compound and
other nitride semiconductor layer, other semiconductor layer or the
like may be used. When the substrate 21 of the LED 2 is an
insulating substrate, connection to the pair of the terminal
electrodes 11 and 12 which is provided on the insulating substrate
1 described above, is carried out by wire bonding for both or can
be connected directly to both of terminal electrodes 11 and 12 with
adhesive by a face down method.
[0046] Furthermore, the n-type layer 23 and the p-type layer 25 are
not limited to a GaN layer described above, AlGaN based compound or
the like may be used, and, in stead of forming each of the layers
with single layer, complex layers can be formed which are formed
with a material which can easily confine carriers such as AlGaN
based compound having large band gap energy at an active layer side
and a GaN layer or the like which is apt to raise carrier
concentration at an opposite side of the active layer. In addition,
a material for the active layer 24 is selected depending upon a
desired wavelength of light, a structure is not limited to a MQW
structure and a SQW structure or a bulk layer may be formed.
Furthermore, a material of the light transmitting conductive layer
26 is not limited to ZnO, ITO or a thin alloy film having a
thickness of 2 to 100 nm made of Ni and Au can be used, and a
material which can transmit light and diffuse current to whole part
of a chip can be used. A Ni--Au layer is formed thin since the
layer loses light transmission by a metal layer when the layer is
formed thick, however, a ZnO or ITO layer can be allowed to be
thick because they transmit light. Of course, as shown in FIG.
4(b), in case of taking out light from a side of the substrate 21,
the light transmission is not necessary, therefore Ni--Au layer or
the like can be formed thick for the p-side electrode.
[0047] By die bonding (mounting) each of the LED chips 2
respectively on the first bonding section 11a provided on the
through holes 4 (nine places in the example shown in FIG. 1) for
heat dissipation which are connected to the first terminal
electrode, for example, through a connection means such as a
conductive adhesive, the upper electrode (p-side electrode 27) of
each of the LED chips 2 is electrically connected to the first
terminal electrode 11, and an electrode (n-side electrode 28) of
the substrate 21 side of each of the LED chips 2 is electrically
connected to the second bonding section 12a of the second terminal
electrode 12 through a wire 7 made of Au or the like, thereby each
of the chips is connected in parallel by a relationship of the
first terminal electrode 11 and the second terminal electrode
12.
[0048] The reflecting wall 3 and the reflecting case 3a, described
above, are formed on the substrate 1 by a screen printing method, a
glass binder or the like, and the plurality of LED chips 2 are
bonded and wire bonded, thereafter a resin mixed with a light color
conversion member (fluorescent) is filled so as to coat a portion
of each of the LED chips 2 and each of the wires 7 exposed in the
reflecting wall 3, thereby blue light emitted in the LED chips 2
can be converted into white light. Namely, there can be used for
the light color conversion member, a red color conversion member
converting blue light into red light such as yttrium oxide or the
like activated by europium, and a blue color conversion member such
as an aluminate fluorescent material of an alkaline earth group
activated by, for example, bivalent manganese and europium, and a
sealing resin layer not shown in the figures is formed by filling a
light transmitting resin such as a silicone resin, an epoxy resin
or the like mixed with the light color conversion members in the
reflecting wall 3. In addition, when the LED chips 2 emit
ultraviolet light, besides, for example, the above-described light
color conversion member converting ultraviolet light into red light
and green light, by mixing a light color conversion member for
converting ultraviolet light into blue light such as a
halophosphate fluorescent material, an aluminate fluorescent
material or the like using cerium, europium or the like for an
activator, ultraviolet light is converted into red light, green
light and blue light, and white light can be obtained by mixing
them. In addition, in case of not converting light color, the LED
chips are sealed with a light transmitting resin.
[0049] Subsequently, a method for manufacturing the chip type
semiconductor light emitting device will be given below. Firstly,
on a large green sheet (sheet for a large number of devices) having
a thickness of approximately 0.3 mm, penetrations for forming the
through holes 4 for heat dissipation are formed and penetrations
for the through holes la are formed by punching, metal films for
the terminal electrodes 11 and 12 are formed on a surface thereof,
and the penetrations for the through holes 4 for heat dissipation
are filled with a metal material such as Ag or the like, thereby
the substrate 1 on which a pattern of the terminal electrodes shown
in FIG. 2(b) is formed. In addition, on the back surface of the
green sheet, the back surface electrodes 11b and 12b are provided
so as to be connected to the terminal electrodes 11 and 12 formed
on the surface of the substrate 1.
[0050] Subsequently, for example, by a screen printing method or
the like, a paste of alumina powder is coated so as to surround
each of positions on the substrate where chips are provided and
dried thereafter. By using a mask having slightly smaller openings,
the paste of alumina is further coated thereon and dried. This
process is repeated several times, the reflecting wall 3 is
laminated stepwise so as to be gradually narrower toward the front
surface, and thereafter sintered at a temperature of approximately
600 to 700.degree. C., thereby the reflecting wall 3 is formed of a
sintered body of alumina and with a grid shape, together with the
substrate 1. In addition, there may be another method such that the
reflecting wall 3 except at a circumference of the chip type
semiconductor light emitting device is formed by the
above-described screen printing method, and as for the reflecting
case 3a of the circumference, for example, the reflecting case 3a
formed porous with a sintered body of alumina is stuck with a glass
binder or the like. By forming porous, a reflection coefficient and
heat dissipation property are improved. The reflecting wall 3 has
an object to reflect light traveling laterally so as to emit light
which is emitted from the LED chips 2 toward the front surface side
totally. In addition, in case of forming the substrate 1 and the
reflecting wall 3 with a white resin without using the sintered
body of alumina, after coating and laminating, adhesion can be
achieved by baking at a temperature of approximately several
hundreds .degree. C.
[0051] Thereafter, the LED chips 2 emitting blue light or
ultraviolet light are mounted on the first bonding sections 11a
provided on the through holes 4 for heat dissipation on a surface
of the insulating substrate 1, and the electrodes (a p-side
electrode and an n-side electrode) of each of the LED chips are
electrically connected respectively. In the example shown in FIG.
1, the p-side electrode of each of the LED chips 2 is connected to
the first bonding section 11a through an electrically conductive
adhesive or the like, thereby the p-side electrode is electrically
connected to the first terminal electrode 11 through the through
hole 4 for heat dissipation, and the n-side electrode (electrode of
a side of the substrate) are electrically connected to the second
terminal electrodes 12 by bonding using a connection means such as
a wire 7 or the like.
[0052] Thereafter, the sealing resin layer including light color
conversion members is formed by coating so as to coat exposed
surfaces of the front surface of each of the LED chips 2 and inner
surfaces of the reflecting wall 3 by, for example, a dispenser or
the like. The sealing resin is formed with, for example, a resin
mixed with a green light conversion member converting blue light
into green light and a red color conversion member converting blue
light into red light. As a coating method, a transfer method by a
transfer pin may be used in place of coating by the dispenser.
[0053] As described above, the present invention is characterized
in a structure in which the plurality of LED chips 2 formed by
dividing a conventional LED chip small are provided on the
substrate 1 and the reflecting wall 3 are provided at a surrounding
of each of the LED chips 2. Namely, since each of the LED chips 2
emits light all around from a light emitting portion, light is
usually emitted upward and also from sides. Then, since the light
emitted from the sides is reflected upward by the reflecting wall
3, the light from the sides can contribute to light emitting
without any waste. In addition, according to the present invention,
not by using one large chip as conventional, but by dividing the
chip into the small LED chips 2 and providing the reflection wall 3
at the surrounding of each of the LED chips 2, area of the sides
can be enlarged compared to the conventional structure, and a total
quantity of the light emitted from the sides can be increased.
[0054] In addition, if one large chip is used and a reflecting case
is provided at a surrounding thereof, light attenuates by
absorption or the like during traveling from the inside of the chip
to sides, and, at the same time, even as for the light emitted from
the sides, since a distance of the chip and the reflecting case is
large, a loss of light in the light emitted from the sides may
occur during traveling to the reflecting case. However, by the
present invention, since the LED chips 2 are formed small by being
divided and provided separately, and the reflecting wall 3 is
provided at the surrounding of each of the LED chips 2, attenuation
in each of the LED chips 2 is small, the light can be reflected
almost perfectly upward at the reflecting wall 3 because the
distance of the chip and the reflecting wall is small and the loss
of the light hardly occurs. As a result, concretely, luminance can
be improved by approximately 20% compared to the case of using one
large chip. In addition, by forming the LED chips by being divided
with small size, it is supposed that area of the surface covered by
wire bonding increases because wire bonding of each LED chip is
necessary, however, also in case of one large LED chip, it is
necessary to provide metal wiring from a wire bonding section
radially in order to spread current to the entire chip, and the
loss thereby is not so different.
[0055] In addition, not by surrounding only a periphery of the
entire chip type semiconductor light emitting device, but by
providing individually the reflection wall 3 at a periphery of each
of the plurality of LED chips 2 provided on the substrate, light
emitted from each of the LED chips 2 is reflected upward by the
reflecting wall 3 near each of the LED chips respectively. In
addition, since regions separated by the reflecting wall 3 are
divided small corresponding to number of the chips, point light
sources are dispersed in a surface. As a result, an entire of a
large region of the substrate 1 emits light uniformly, as the chip
type semiconductor light emitting device, distribution of luminance
in the surface becomes extremely uniform, and the distribution of
luminance in the surface is significantly improved compared to that
in case of using one conventional large chip.
[0056] Furthermore, as in a conventional type, if a chip of a large
size is used and the reflecting case is provided at a periphery of
the substrate, thermal conduction is inferior in the chip at a time
of large current drive, and heat can not be dissipated sufficiently
through the reflecting case because a distance from the chip to the
reflecting case is large, then there arises a problem of
deterioration of reliability caused by deterioration of the chip by
the heat. In the present invention, by dividing into a plurality of
LED chips 2, and providing on the substrate 1 dispersed, and
providing the reflecting wall 3 at the vicinity thereof, the heat
generated in each of the LED chips 2 can be dissipated through the
reflecting wall 3 right soon. In addition, since the LED chips are
provided on the substrate 1 dispersed, a region of generating heat
is dispersed in a large area of the substrate, then deterioration
by the heat can be prevented.
[0057] In the above-described example, in order to emit white light
by using a LED chip emitting blue light or ultraviolet light, a
light color conversion resin is used for a sealing resin to protect
a wire or the like, however the present invention is not limited to
the white light emitting device and can be applied to semiconductor
light emitting devices being apt to generate heat at high
luminance.
INDUSTRIAL APPLICABILITY
[0058] The present invention can be used for light sources of a
wide field such as backlights for liquid display devices or the
like, light emitting devices of various kinds for white light, blue
light or the like, and lighting devices or the like.
* * * * *